WASHINGTON  Microsoft Corp. and other leading Internet companies, in an unusual joint effort among corporate rivals, announced six lawsuits today against hundreds of people accused of sending millions of unwanted e-mails in violation of the new federal law against "spam."

The legal actions by Microsoft, America Online Inc., Earthlink Inc. and Yahoo! Inc., represent the first major industry actions under the "can spam" legislation that went into effect Jan. 1. The suits were filed in federal courts in California, Georgia, Virginia and Washington state.

Dozens of those named were identified only as "John Doe" defendants accused of e-mailing unwanted pitches for prescription drugs, herbal potions and weight loss plans. Lawyers expressed confidence they can work through the courts, using subpoenas and other investigative tools, to identify and find them.

"We've been doing this a long time, and we know what we're doing. We're only a couple subpoenas away from standing at someone's door and handing them a summons," said Les Seagraves, the assistant general counsel at Earthlink, which named 75 "John Doe" defendants in its lawsuits.

The recording industry has been remarkably successful in identifying Internet users in copyright infringement lawsuits, in most cases tracing a subscriber's unique Internet address.

But spammers are famously skillful at covering their tracks, often routing unwanted e-mails through hacked or unprotected computers overseas and working under aliases and shell companies, complicating efforts to trace and identify them.

Yahoo, for example, employed as one of its lawyers in these cases Marc Zwillinger, a former computer-crimes expert at the Justice Department who investigated the high-profile Internet attacks in February 2000 by a Canadian teenager known as Mafia Boy.

"It is a significant challenge," acknowledged H. Robert Wientzen, chief executive at the Direct Marketing Association, who said he supports the latest lawsuits. He said companies are increasingly successful tracing spammers. "We're making some progress with techniques and tools that are starting to pay some dividends," Wientzen said.

The four companies said the defendants include some of the nation's most notorious large-scale spammers. They said they shared information, resources and investigative information to identify some of them.

Among the named defendants were Davis Wolfgang Hawke of Medfield, Mass., whom AOL lawyers said also is known as Dave Bridger, and Braden Bournival of Manchester, N.H. They and others were accused of sending millions of e-mails offering weight loss supplements, handheld devices called "personal lie detectors" and other products.

Hawke did not return a telephone call from The Associated Press to his home in Massachusetts. Bournival moved six months ago from the address in New Hampshire listed in the lawsuit and the woman living there told the AP she did not know how to contact him.

Yahoo sued Eric Daniel Head, Matthew Head and Barry Head, all of Ontario, Canada. It said they run Golddisk.net and at least four other companies, all of which identify Eric Head as an officer or director. Yahoo accused the Heads of sending 94 million e-mails to its subscribers since Jan. 1, soliciting people to visit Web sites registered to false Chinese names and addresses.

The Heads also could not be reached for comment. Five telephone numbers listed in the lawsuit were either disconnected or reassigned to new customers.

The "can spam" legislation requires unsolicited e-mails to include a mechanism so recipients could indicate they did not want future mass mailings.

The law also prohibits senders of unsolicited commercial e-mail from disguising their identity by using a false return address or misleading subject line, and it prohibits senders from harvesting addresses off Web sites.